Composite materials are widely used for aerospace applications. While structural composites are becoming more prevalent in airframe design, composites have long been used for various components of an aircraft's interior, primarily because of the material's light weight and high strength-to-weight ratio. Aircraft interiors may be less demanding structurally when compared to airframe parts, but they are still subject to demanding performance requirements such as mechanical strength, dimensional stability and low heat release in the event of a fire.
The most widely used composite application for aircraft interiors are sandwich structures, commonly referred to as sandwich panels. Sandwich panels are made using a thick, lightweight core sandwiched between two thin face sheets (e.g., plies of a fiber-reinforced material pre-impregnated with a matrix material), which increases the panel's stiffness with little added weight. Sandwich panels are cost-effective because the core material is less expensive and weighs less than the composite face sheets and can be cured or processed with the face sheets in a single operation. Sandwich panels are commonly used for flooring, ceilings, sidewalls, lavatories, stow bins, cargo hold liners and the like.
Flat sandwich panels are typically fabricated with flat press molding conducted at a high temperature and high pressure, in which a cored laminate is placed in a large press and crushed down to a predetermined thickness in a process commonly referred to as “crush core.” Crush core is an efficient and economical process for fabrication of sandwich panels. One disadvantage to the core crush process is it is a non-continuous process in which individual sandwich panels are fabricated and trimmed. Another disadvantage to the crush core process is the challenge of fabricating sandwich panels within applicable tolerances. Otherwise, a costly and lengthy re-work process may be required or material waste may result if the damage is so extensive that it is beyond repair.
Further, many interior parts can include contoured shapes or other non-planar (e.g., complex) shapes. These contoured shapes are typically made from flat sandwich panels by a cut and fold process. In this process, a portion of one face sheet is removed to expose the core. Adhesive is then applied to the exposed core and the sandwich panel is folded to the desired position and clamped until the adhesive cures. While this process is economical, one disadvantage is the material waste associated with the cut and fold and the challenge of consistent fabrication of panels within the applicable tolerances.
Following final inspection of the sandwich panel, desired surface decorations are applied to individual sandwich panels. Examples of decorative surfaces typically include plastic films or paint. However, painting requires additional surface preparation steps, such as filling, sanding and primer application. A decorative film eliminates some of the surface-prep and finishing steps, but may add cost and weight to the part.
Accordingly, those skilled in the art continue with research and development efforts in the field of composite sandwich panels.